1. Field of the Invention
The present invention relates an apparatus for manufacturing a solid electrolytic capacitor particularly of a kind having a solid electrolytic layer made of an electroconductive polymer.
2. Description of the Related Art
In recent years, rapid progress has been made in high-speed digital signal processing and multimedia appliances have come to have a high-speed feature along with a compact size. The need has incidentally increased to use downsized and flattened power supplies for high-frequency driving and, therefore, stabilization and noise reduction have now come to be an important factor. Under these circumstances, a solid electrolytic capacitor, an important circuit component part, is desired to have a low ESR (equivalence series resistance) so that it can adapt to a rapid change in voltage, and also to have a compact size and a large capacity so that it can be surface mounted.
A solid electrolytic capacitor of a kind having a solid electrolytic layer made of an electroconductive polymer can meet the requirement. Hereinafter, the solid electrolytic capacitor will be discussed.
FIG. 12A illustrates a sectional representation of the standard solid electrolytic capacitor 60. The solid electrolytic capacitor 60 includes a capacitor element 45 embedded in a covering resin 49 with respective portions of anode and cathode terminals 46 and 47 exposed to the outside thereof.
The capacitor element 45 is made up of a porous anode element 40, a dielectric oxide film 42 formed on a surface of the anode element 40, a solid electrolytic layer 43 formed over the dielectric oxide film 42 and a cathode layer 44 formed over the solid electrolytic layer 43. FIG. 12B is a fragmentary enlarged diagram showing the anode element 40. The porous anode element 40 has a plurality of micropores 62 on its surface as shown in FIG. 12B.
The porous anode element 40 is obtained by pressing a powder of a valve action metal, for example, tantalum to a desired shape and then sintering it, and the anode element 40 has embedded therein an anode lead line 41 in the form of a tantalum wire with a portion of the anode lead line exposed to the outside. The anode lead line 41 is connected with the anode terminal 46. The dielectric oxide film 42 is obtained by anodizing the surface of the anode element 40. The solid electrolytic layer 43 is made of an electroconductive polymer such as polypyrrole. The anode terminal 46 is connected with the anode lead line 41 by welding and the cathode terminal 47 is connected with the cathode layer 44 by the use of an electroconductive bonding agent 48. The exposed portions of the anode and cathode terminals 46 and 47 are bent inwardly so that the capacitor 60 can be surface-mountable as a capacitor chip on a planar support surface.
A method of manufacturing the solid electrolytic capacitor 60 will be discussed with reference to a flowchart of FIG. 13 showing the sequence of making the solid electrolytic capacitor 60 according to the prior art.
As shown therein the tantalum metal powder with the anode lead line 41 embedded therein is pressed to a desired shape and is then sintered to provide the porous anode element 40(Shaping and Sintering Step).
Subsequently, using a phosphoric acid, the anode element 40 is anodized to form the dielectric oxide film 42 on an outer surface of the anode element 40(Anodizing Step).
After the anode element 40 has been impregnated with a pyrrole monomer solution, the anode element 40 is dipped into a solution with an oxidizing agent, or after the anode element 40 has been dipped into the solution with the oxidizing agent, the anode element 40 is impregnated with a pyrrole monomer solution and the solid electrolytic layer 43 is formed over the dielectric oxide film 42 by means of a chemical oxidation polymerization(Polymerization Step).
Thereafter, carbon is coated, a silver paint is coated and drying is performed to complete formation of the cathode layer 44, thereby completing the capacitor element 45(Cathode Forming Step).
Then, the anode lead line 41 extending from the capacitor element 45 is welded to the anode terminal 46 of a lead frame and the cathode layer 44 is connected with the cathode terminal 47 by the use of an electroconductive bonding agent 48(Fabrication Step). The capacitor element 45 is thereafter resin-molded in an epoxy covering resin 49 with respective portions of the anode and cathode terminals 46 and 47 exposed to the outside of the covering resin 49(Resin-encasing Step). In general, by the sequence discussed above, a batch of capacitors 60 are manufactured at a time with the anode and cathode terminals 46 and 47 of one capacitor 60 continuous with those of the next adjacent capacitor 60. Accordingly, as a final step, the capacitors 60 connected together are separated into the individual capacitors 60 which are subsequently tested to provide the individual solid electrolytic capacitors 60(Finishing Step).
FIG. 14 shows a schematic layout of a portion of the capacitor manufacturing apparatus where polymerization is carried out, and FIG. 15 is a fragmentary enlarged perspective view of the polymerization part of FIG. 14. As shown in FIG. 14, the polymerization part includes one first array of baths 50 and 50A, four second arrays of baths 50 and 50A, and two third arrays of baths 50 and 50A, and these first, second, and third arrays are arranged in parallel. These arrays include a plurality of polymerization baths 50, and baths 50A for cleansing, drying, and so on. The first array is a polymerization (A) process line for forming the solid electrolytic layer 43 made of polypyrrole on an outer surface 63 (FIG. 12B) of the anode element 40 (that is, the surface except for the micropores 62 of the anode element 40) by means of a chemical oxidation polymerization. The second lines are polymerization (B) process lines for forming the solid electrolytic layer 43 made of polypyrrole within the micropores of the anode element 40 by means of a chemical oxidation polymerization. The third lines are polymerization (C) process lines for forming the solid electrolytic layer 43 made of an electroconductive polymer such as polythiophene, which is different from polypyrrole, by means of a chemical oxidation polymerization.
Each of the first, second, and third lines includes a plurality of polymerization baths 50 as shown in FIG. 14. As shown in FIGS. 14 and 15, the polymerization baths 50 are arranged in line and connected, and a conveyance between the baths was performed manually by an attendant worker 61.
It is difficult to form the solid electrolytic layer 43 within the micropores 62 as well as on the outer surface 63 of the anode element 40, and the solid electrolytic layer 43 having a desired thickness cannot be formed by one polymerization step. Accordingly, since each of the processes is required to be repeated several ten times, a considerably complex process such as 3 repetitions of the polymerization process A and 14 repetitions of the polymerization process B for each of the 4 lines, has been required.
FIGS. 16A and 16B are a plan view and a sectional view, respectively, of the polymerization bath 50 which is used for a chemical oxidation polymerization in the polymerization process. In FIG. 16A, the polymerization bath 50 has an open-topped cavity 64, a supply passage 51 for supplying the cavity 64 with a polymerization solution 54 from a tank (not shown) of the polymerization solution 54, the supply passage 51 being defined at a center of the bottom surface of the cavity 64 and communicated with the cavity 64, weir boards 52A and 52B which are placed in the cavity 64, and waste liquid tubes 53A and 53B for draining an overflow of the polymerization solution 54 over the weir boards 52A and 52B.
Hereinafter, an operation of the polymerization bath 50 will be described. At first, the polymerization solution 54 is supplied from the solution tank (not shown) into the cavity 64 through the supply passage 51 so as to fill the cavity 64 with the polymerization solution 54. The polymerization solution 54 which is supplied to the cavity 64 in an amount greater than a predetermined amount overflows the weir boards 52A and 52B and is then drained out of the cavity 64.
However, the conventional apparatus for manufacturing the solid electrolytic capacitor above has the following problems.
In the first place, the conventional apparatus makes use of a belt-type conveyor for successively transporting pallets linearly at the polymerization station where complicated and laborious polymerization processes are performed and, therefore, the apparatus is bulky having a substantial length and expensive to manufacture while requiring a relatively large space for installation.
Secondly, in the case where an accident happens in the subsequent processes halfway, all of the lines have to be brought to a halt, resulting in reduction in operation rate which would in turn result in defective products. Accordingly, the productivity is considerably reduced.
Finally, since the polymerization solution 54 bubbles in the cavity 64 during the filling of the bath 50 with the polymerization solution 54, the bubbles adversely affect the polymerization process, resulting in a non-uniform formation of the solid electrolytic layer 43. In order to prevent the occurrence of the bubbles, it was proposed to reduce the speed for supplying the polymerization solution 54 into the cavity 64. This, however, makes an operating efficiency considerably lower, and it is still difficult to completely avoid the occurrence of the bubbles even though the supplying speed of the polymerization solution 54 is reduced. In addition, since the polymerization solution 54 circulates unevenly within the cavity 64, it is difficult to control the surface level and the temperature of the polymerization solution 54, resulting that the polymerization process is also adversely affected and the solid electrolytic layer 43 cannot be uniformly formed.
In view of the foregoing numerous problems, the present invention has been devised to eliminate the foregoing problems and is to provide an apparatus for manufacturing a solid electrolytic capacitor, which is compact in size and which is effective to prevent a production of defective products and to exhibit an excellent productivity with a low cost owing to the use of a polymerization bath which is effective to prevent an occurrence of bubbles and in which the surface level and the temperature of the polymerization solution can easily be controlled while allowing a solid electrolytic layer to be formed uniformly.
According to one aspect of the invention, an apparatus for manufacturing a solid electrolytic capacitor includes: (1) an anodization part for forming a dielectric oxide film on a surface of a porous anode element made of a valve action metal, the anode element having embedded therein an anode lead line with one end portion of the anode lead line exposed to an outside; (2) a polymerization part for forming a solid electrolytic layer made of an electroconductive polymer on the dielectric oxide film by a chemical oxidation polymerization, and comprising a plurality of polymerization baths of a substantially same structure, and a conveyance mechanism, wherein the plurality of polymerization baths are placed around the conveyance mechanism within a conveyance range; (3) a cathode layer formation part for forming a cathode layer on the solid electrolytic layer and providing a capacitor element; (4) an assembly part for connecting the anode lead line with an anode terminal and connecting the cathode lead line with a cathode terminal, the anode and cathode terminals being for connecting with an outer circuit; and (5) a molding part for covering the capacitor element with a covering resin with respective portions of the anode and cathode terminals exposed to an outside.
According to the above manufacturing apparatus, since the polymerization part has the plurality of polymerization baths of the substantially same structure, and the conveyance mechanism, and the plurality of polymerization baths are placed around the conveyance mechanism within a conveyance range, the manufacturing apparatus can be assembled compactly with the polymerization part unitized together with the constituent baths. In addition, since each of the plurality of the polymerization baths can be independent, all lines of the production processes do not have to be halted even if an accident happens in a subsequent production process halfway, making it possible to improve an operation rate, yield, and productivity.
According to another aspect of the invention, at least one of the polymerization baths includes: a first open-topped cavity to be filled with a polymerization solution; a supply passage for supplying the first open-topped cavity with the polymerization solution, the supply passage being located at one end of a bottom surface of the first open-topped cavity and communicated with the first open-topped cavity; an interruptible jet plate for preventing a jet flow of the polymerization solution supplied through the supply passage, and the interruptible jet plate being located adjacent to a connection part of the supply passage and the first open-topped cavity; a guide plate for restraining a rise of a level of the polymerization solution which is supplied to the first open-topped cavity via the interruptible jet plate, and the guide plate being located from one end of the first open-topped cavity adjacent to the interruptible jet plate to a substantially center position of the first open-topped cavity; and a level controlling mechanism for controlling the level of the polymerization solution supplied into the first open-topped cavity at a predetermined amount.
According to the above manufacturing apparatus, since the polymerization bath has the above-described interruptible jet plate and guide plate, it is possible to prevent an occurrence of the bubbles in the polymerization solution during when the cavity of the bath is supplied with the polymerization solution. Accordingly, the cavity can be filled with the polymerization solution while the polymerization solution is prevented from bubbling and the level of the polymerization solution 21 is continuously controlled precisely, and hence, the operation efficiency can be improved and the solid electrolytic layer can be uniformly formed.